The two hard deadlines are non-negotiable. The seller has 45 calendar days from closing the relinquished property to formally identify replacement property (in writing, to the qualified intermediary), and 180 calendar days from closing to actually take title to the replacement. Both clocks run from the same date and there is no extension for weekends, holidays or closing delays — only federally declared disaster relief.
The practical effect on broker workflows is that a 1031 buyer is on the clock from day one. Time-pressured 1031 buyers will overpay slightly for certainty (deals that can close inside the 180-day window), and a broker who knows which inventory matches a 1031 buyer's identification list, value range and boot target is far more useful than one who just sends generic inventory.
